To assess the metabolic effects of systematic variation in protein intake in newborn infants receiving total parenteral nutrition by measurement of weight gain, degree of positive nitrogen balance, plasma and urine amino acid patterns and change in body water spaces (using D2O and Br-). To study the dynamics of nitrogen metabolism in such infants using N15 labelled urea and arginine and to develop a model for the kinetics of nitrogen metabolism under these conditions. To study the plasma and urine RNase in infants receiving total parenteral nutrition as indicators of nutritional adequacy. To ascertain the essential fatty acid status of infants receiving total parenteral nutrition with infusates containing no lipid whatsoever.